High resolution thin multi-aperture imaging systems

ABSTRACT

A multi-aperture imaging system comprising a first camera with a first sensor that captures a first image and a second camera with a second sensor that captures a second image, the two cameras having either identical or different FOVs. The first sensor may have a standard color filter array (CFA) covering one sensor section and a non-standard color CFA covering another. The second sensor may have either Clear or standard CFA covered sections. Either image may be chosen to be a primary or an auxiliary image, based on a zoom factor. An output image with a point of view determined by the primary image is obtained by registering the auxiliary image to the primary image.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Phase application from PCT patentapplication PCT/IB2013/060356 which claims priority from U.S.Provisional Patent Application No. 61/730,570 having the same title andfiled Nov. 28, 2013, which is incorporated herein by reference in itsentirety.

FIELD

Embodiments disclosed herein relate in general to multi-aperture imaging(“MAI”) systems (where “multi” refers to two or more apertures) and morespecifically to thin MAI systems with high color resolution and/oroptical zoom.

BACKGROUND

Small digital cameras integrated into mobile (cell) phones, personaldigital assistants and music players are becoming ubiquitous. Each year,mobile phone manufacturers add more imaging features to their handsets,causing these mobile imaging devices to converge towards feature setsand image quality that customers expect from stand-alone digital stillcameras. Concurrently, the size of these handsets is shrinking, makingit necessary to reduce the total size of the camera accordingly whileadding more imaging features. Optical Zoom is a primary feature of manydigital still cameras but one that mobile phone cameras usually lack,mainly due to camera height constraints in mobile imaging devices, costand mechanical reliability.

Mechanical zoom solutions are common in digital still cameras but aretypically too thick for most camera phones. Furthermore, the F/# (“Fnumber) in such systems typically increases with the zoom factor (ZF)resulting in poor light sensitivity and higher noise (especially inlow-light scenarios). In mobile cameras, this also results in resolutioncompromise, due to the small pixel size of their image sensors and thediffraction limit optics associated with the F/#.

One way of implementing zoom in mobile cameras is by over-sampling theimage and cropping and interpolating it in accordance with the desiredZF. While this method is mechanically reliable, it results in thickoptics and in an expensive image sensor due to the large number ofpixels associated therewith. As an example, if one is interested inimplementing a 12 Megapixel camera with X3 ZF, one needs a sensor of 108Megapixels.

Another way of implementing zoom, as well as increasing the outputresolution, is by using a dual-aperture imaging (“DAI”) system. In itsbasic form, a DAI system includes two optical apertures which may beformed by one or two optical modules, and one or two image sensors(e.g., CMOS or CCD) that grab the optical image or images and convertthe data into the electronic domain, where the image can be processedand stored.

The design of a thin MAI system with improved resolution requires acareful choice of parameters coupled with advanced signal processingalgorithms to support the output of a high quality image. Known MAIsystems, in particular ones with short optical paths, often trade-offfunctionalities and properties, for example zoom and color resolution,or image resolution and quality for camera module height. Therefore,there is a need for, and it would be advantageous to have thin MAIsystems that produce an image with high resolution (and specificallyhigh color resolution) together with zoom functionality.

Moreover, known signal processing algorithms used together with existingMAI systems often further degrade the output image quality byintroducing artifacts when combining information from differentapertures. A primary source of these artifacts is the image registrationprocess, which has to find correspondences between the different imagesthat are often captured by different sensors with different color filterarrays (CFAs). There is therefore a need for, and it would beadvantageous to have an image registration algorithm that is more robustto the type of CFA used by the cameras and which can produce bettercorrespondence between images captured by a multi-aperture system.

SUMMARY

Embodiments disclosed herein teach the use of multi-aperture imagingsystems to implement thin cameras (with short optical paths of less thanabout 9 mm) and/or to realize optical zoom systems in such thin cameras.Embodiments disclosed herein further teach new color filter arrays thatoptimize the color information which may be achieved in a multi-apertureimaging system with or without zoom. In various embodiments, a MAIsystem disclosed herein includes at least two sensors or a single sensordivided into at least two areas. Hereinafter, the description refers to“two sensors”, with the understanding that they may represent sectionsof a single physical sensor (imager chip). Exemplarily, in adual-aperture imaging system, a left sensor (or left side of a singlesensor) captures an image coming from a first aperture while a rightsensor (or right side of a single sensor) captures an image coming froma second aperture. In various embodiments disclosed herein, one sensoris a “Wide” sensor while another sensor is a “Tele” sensor, see e.g.FIG. 1A. The Wide sensor includes either a single standard CFA or twodifferent CFAs: a non-standard CFA with higher color sampling ratepositioned in an “overlap area” of the sensor (see below description ofFIG. 1B) and a standard CFA with a lower color sampling rate surroundingthe overlap area. When including a single standard CFA, the CFA maycover the entire Wide sensor area. A “standard CFA” may include a RGB(Bayer) pattern or a non-Bayer pattern such as RGBE, CYYM, CYGM, RGBW#1,RGBW#2 or RGBW#3. Thus, reference may be made to “standard Bayer” or“standard non-Bayer” patterns or filters. As used herein, “non-standardCFA” refers to a CFA that is different in its pattern that CFAs listedabove as “standard”. Exemplary non-standard CFA patterns may includerepetitions of a 2×2 micro-cell in which the color filter order isRR-BB, RB-BR or YC-CY where Y=Yellow=Green+Red, C=Cyan=Green+Blue;repetitions of a 3×3 micro-cell in which the color filter order isGBR-RGB-BRG; and repetitions of a 6×6 micro-cell in which the colorfilter order is

RBBRRB-RWRBWB-BBRBRR-RRBRBB-BWBRWR-BRRBBR, or

BBGRRG-RGRBGB-GBRGRB-RRGBBG-BGBRGR-GRBGBR, or

RBBRRB-RGRBGB-BBRBRR-RRBRBB-BGBRGR-BRRBBR, or,

RBRBRB-BGBRGR-RBRBRB-BRBRBR-RGRBGB-BRBRBR.

The Tele sensor may be a Clear sensor (i.e. a sensor without colorfilters) or a standard CFA sensor. This arrangement of the two (or morethan two) sensors and of two (or more than two) Wide and Tele “subsetcameras” (or simply “subsets”) related to the two Wide and Tele subsets.Each sensor provides a separate image (referred to respectively as aWide image and a Tele image), except for the case of a single sensor,where two images are captured (grabbed) by the single sensor (exampleabove). In some embodiments, zoom is achieved by fusing the two images,resulting in higher color resolution that approaches that of a highquality dual-aperture zoom camera. Some thin MAI systems disclosedherein therefore provide zoom, super-resolution, high dynamic range andenhanced user experience.

In some embodiments, in order to reach optical zoom capabilities, adifferent magnification image of the same scene is grabbed by eachsubset, resulting in field of view (FOV) overlap between the twosubsets. In some embodiments, the two subsets have the same zoom (i.e.same FOV). In some embodiments, the Tele subset is the higher zoomsubset and the Wide subset is the lower zoom subset. Post processing isapplied on the two images grabbed by the MAI system to fuse and outputone fused (combined) output zoom image processed according to a user ZFinput request. In some embodiments, the resolution of the fused imagemay be higher than the resolution of the Wide/Tele sensors. As part ofthe fusion procedure, up-sampling may be applied on the Wide image toscale it to the Tele image.

In an embodiment there is provided a multi-aperture imaging systemcomprising a first camera subset that provides a first image, the firstcamera subset having a first sensor with a first plurality of sensorpixels covered at least in part with a non-standard CFA, thenon-standard CFA used to increase a specific color sampling raterelative to a same color sampling rate in a standard CFA; a secondcamera subset that provides a second image, the second camera subsethaving a second sensor with a second plurality of sensor pixels eitherClear or covered with a standard CFA; and a processor configured toprocess the first and second images into a combined output image.

In some embodiments, the first and the second camera subsets haveidentical FOVs and the non-standard CFA may cover an overlap area thatincludes all the pixels of first sensor, thereby providing increasedcolor resolution. In some such embodiments, the processor is furtherconfigured to, during the processing of the first and second images intoa combined output image, register respective first and second Lumaimages obtained from the first and second images, the registered firstand second Luma images used together with color information to form thecombined output image. In an embodiment, the registration includesfinding a corresponding pixel in the second Luma image for each pixel inthe first Luma image, whereby the output image is formed by transferringinformation from the second image to the first image. In anotherembodiment, the registration includes finding a corresponding pixel inthe first Luma image for each pixel in the second Luma image, wherebythe output image is formed by transferring information from the firstimage to the second image.

In some embodiments, the first camera subset has a first FOV, the secondcamera subset has a second, smaller FOV than the first FOV, and thenon-standard CFA covers an overlap area on the first sensor thatcaptures the second FOV, thereby providing both optical zoom andincreased color resolution. In some such embodiments, the processor isfurther configured to, during the processing of the first and secondimages into a combined output image and based on a ZF input, registerrespective first and second Luma images obtained from the first andsecond images, the registered first and second Luma images used togetherwith color information to form the combined output image. For a ZF inputthat defines an FOV greater than the second FOV, the registrationincludes finding a corresponding pixel in the second Luma image for eachpixel in the first Luma image and the processing includes forming theoutput image by transferring information from the second image to thefirst image. For a ZF input that defines an FOV smaller than or equal tothe second FOV, the registration includes finding a corresponding pixelin the first Luma image for each pixel in the second Luma image, and theprocessing includes forming the output image by transferring informationfrom the first image to the second image.

In an embodiment there is provided a multi-aperture imaging systemcomprising a first camera subset that provides a first image, the firstcamera subset having a first sensor with a first plurality of sensorpixels covered at least in part with a standard CFA; a second camerasubset that provides a second image, the second camera subset having asecond sensor with a second plurality of sensor pixels either Clear orcovered with a standard CFA; and a processor configured to registerfirst and second Luma images obtained respectively from the first andsecond images and to process the registered first and second Luma imagestogether with color information into a combined output image.

In some embodiments, the first and the second camera subsets haveidentical first and second FOVs. In some such embodiments, theregistration includes finding a corresponding pixel in the second Lumaimage for each pixel in the first Luma image and the processing includesforming the output image by transferring information from the secondimage to the first image. In other such embodiments, the registrationincludes finding a corresponding pixel in the first Luma image for eachpixel in the second Luma image and the processing includes forming theoutput image by transferring information from the first image to thesecond image.

In some embodiments, the first camera subset has a first FOV, the secondcamera subset has a second, smaller FOV than the first FOV, and theprocessor is further configured to register the first and second Lumaimages based on a ZF input. For a ZF input that defines an FOV greaterthan the second FOV, the registration includes finding a correspondingpixel in the second Luma image for each pixel in the first Luma imageand the processing includes forming the output image by transferringinformation from the second image to the first image. For a ZF inputthat defines an FOV smaller than or equal to the second FOV, theregistration includes finding a corresponding pixel in the first Lumaimage for each pixel in the second Luma image, and the processingincludes forming the output image by transferring information from thefirst image to the second image.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting examples of embodiments disclosed herein are describedbelow with reference to figures attached hereto that are listedfollowing this paragraph. The drawings and descriptions are meant toilluminate and clarify embodiments disclosed herein, and should not beconsidered limiting in any way.

FIG. 1A shows schematically a block diagram illustrating a dual-aperturezoom imaging system disclosed herein;

FIG. 1B shows an example of an image captured by the Wide sensor and theTele sensor while illustrating the overlap area on the Wide sensor;

FIG. 2 shows schematically an embodiment of a Wide sensor that may beimplemented in a dual-aperture zoom imaging system disclosed herein;

FIG. 3 shows schematically another embodiment of a Wide camera sensorthat may be implemented in a dual-aperture zoom imaging system disclosedherein;

FIG. 4 shows schematically yet another embodiment of a Wide camerasensor that may be implemented in a dual-aperture zoom imaging systemdisclosed herein;

FIG. 5 shows schematically yet another embodiment of a Wide camerasensor that may be implemented in a dual-aperture zoom imaging systemdisclosed herein;

FIG. 6 shows schematically yet another embodiment of a Wide camerasensor that may be implemented in a dual-aperture zoom imaging systemdisclosed herein;

FIG. 7 shows schematically yet another embodiment of a Wide camerasensor that may be implemented in a dual-aperture zoom imaging systemdisclosed herein;

FIG. 8 shows schematically yet another embodiment of a Wide camerasensor that may be implemented in a dual-aperture zoom imaging systemdisclosed herein;

FIG. 9 shows schematically yet another embodiment of a Wide camerasensor that may be implemented in a dual-aperture zoom imaging systemdisclosed herein;

FIG. 10 shows a schematically in a flow chart an embodiment of a methoddisclosed herein for acquiring and outputting a zoom image;

FIG. 11A shows exemplary images captured by a triple aperture zoomimaging system disclosed herein;

FIG. 11B illustrates schematically the three sensors of the tripleaperture imaging system of FIG. 11A.

DETAILED DESCRIPTION

Embodiments disclosed herein relate to multi-aperture imaging systemsthat include at least one Wide sensor with a single CFA or with twodifferent CFAs and at least one Tele sensor. The description continueswith particular reference to dual-aperture imaging systems that includetwo (Wide and Tele) subsets with respective sensors. A three-apertureimaging system is described later with reference to FIGS. 11A-11B.

The Wide sensor includes an overlap area (see description of FIG. 1B)that captures the Tele FOV. The overlap area may cover the entire Widesensor or only part of the sensor. The overlap area may include astandard CFA or a non-standard CFA. Since the Tele image is opticallymagnified compared to the Wide image, the effective sampling rate of theTele image is higher than that of the Wide image. Thus, the effectivecolor sampling rate in the Wide sensor is much lower than the Clearsampling rate in the Tele sensor. In addition, the Tele and Wide imagesfusion procedure (see below) requires up-scaling of the color data fromthe Wide sensor. Up-scaling will not improve color resolution. In someapplications, it is therefore advantageous to use a non-standard CFA inthe Wide overlap area that increases color resolution for cases in whichthe Tele sensor includes only Clear pixels. In some embodiments in whichthe Tele sensor includes a Bayer CFA, the Wide sensor may have a BayerCFA in the overlap area. In such embodiments, color resolutionimprovement depends on using color information from the Tele sensor inthe fused output image.

FIG. 1A shows schematically a block diagram illustrating a dual-aperturezoom imaging (“DAZI”) system 100 disclosed herein. System 100 includes adual-aperture camera 102 with a Wide subset 104 and a Tele subset 106(each subset having a respective sensor), and a processor 108 that fusestwo images, a Wide image obtained with the Wide subset and a Tele imageobtained with the Tele subset, into a single fused output imageaccording to a user-defined “applied” ZF input or request. The ZF isinput to processor 108. The Wide sensor may include a non-standard CFAin an overlap area illustrated by 110 in FIG. 1B. Overlap area 110 issurrounded by a non-overlap area 112 with a standard CFA (for example aBayer pattern). FIG. 1B also shows an example of an image captured byboth Wide and Tele sensors. Note that “overlap” and “non-overlap” areasrefer to parts of the Wide image as well as to the CFA arrangements ofthe Wide sensor. The overlap area may cover different portions of a Widesensor, for example half the sensor area, a third of the sensor area, aquarter of the sensor area, etc. A number of such Wide sensor CFAarrangements are described in more detail with reference to FIGS. 2-9.The non-standard CFA pattern increases the color resolution of the DAZIsystem.

The Tele sensor may be Clear (providing a Tele Clear image scaledrelative to the Wide image) or may include a standard (Bayer ornon-Bayer) CFA. It in the latter case, it is desirable to define primaryand auxiliary sensors based on the applied ZF. If the ZF is such thatthe output FOV is larger than the Tele FOV, the primary sensor is theWide sensor and the auxiliary sensor is the Tele sensor. If the ZF issuch that the output FOV is equal to, or smaller than the Tele FOV, theprimary sensor is the Tele sensor and the auxiliary sensor is the Widesensor. The point of view defined by the output image is that of theprimary sensor.

FIG. 2 shows schematically an embodiment of a Wide sensor 200 that maybe implemented in a DAZI system such as system 100. Sensor 200 has anon-overlap area 202 with a Bayer CFA and an overlap area 204 covered bya non-standard CFA with a repetition of a 4×4 micro-cell in which thecolor filter order is BBRR-RBBR-RRBB-BRRB. In this figure, as well as inFIGS. 3-9, “Width 1” and “Height 1” refer to the full Wide sensordimension. “Width 2” and “Height 2” refer to the dimensions of the Widesensor overlap area. Note that in FIG. 2 (as in following FIGS. 3-5 and7, 8) the empty row and column to the left and top of the overlap areaare for clarity purposes only, and that the sensor pixels follow therethe pattern of the non-overlap area (as shown in FIG. 6). In overlaparea 204, R and B are sampled at ½^(0.5) Nyquist frequency in thediagonal (left to right) direction with 2 pixel intervals instead of at½ Nyquist frequency in a standard Bayer pattern.

FIG. 3 shows schematically an embodiment of a Wide sensor 300 that maybe implemented in a DAZI system such as system 100. Sensor 300 has anon-overlap area 302 with a Bayer CFA and an overlap area 304 covered bya non-standard CFA with a repetition of a 2×2 micro-cell in which thecolor filter order is BR-RB. In the overlap area, R and B are sampled at½^(0.5) Nyquist frequency in both diagonal directions.

FIG. 4 shows schematically an embodiment of a Wide sensor 400 that maybe implemented in a DAZI system such as system 100. Sensor 400 has anon-overlap area 402 with a Bayer CFA and an overlap area 404 covered bya non-standard CFA with a repetition of a 2×2 micro-cell in which thecolor filter order is YC-CY, where Y=Yellow=Green+Red,C=Cyan=Green+Blue. As a result, in the overlap area, R and B are sampledat ½^(0.5) Nyquist frequency in a diagonal direction. The non-standardCFA includes green information for registration purposes. This allowsfor example registration between the two images where the object isgreen, since there is green information in both sensor images.

FIG. 5 shows schematically an embodiment of a Wide sensor 500 that maybe implemented in a DAZI system such as system 100. Sensor 500 has anon-overlap area 502 with a Bayer CFA and an overlap area 504 covered bya non-standard CFA with a repetition of a 6×6 micro-cell in which thecolor filter order is RBBRRB-RWRBWB-BBRBRR-RRBRBB-BWBRWR-BRRBBR, where“W” represents White or Clear pixels. In the overlap area, R and B aresampled at a higher frequency than in a standard CFA. For example, in aBayer pixel order, the Red average sampling rate (“R_(S)”) is 0.25(sampled once for every 4 pixels). In the overlap area pattern, R_(S) is0.44.

FIG. 6 shows schematically an embodiment of a Wide sensor 600 that maybe implemented in a DAZI system such as system 100. Sensor 600 has anon-overlap area 602 with a Bayer CFA and an overlap area 604 covered bya non-standard CFA with a repetition of a 6×6 micro-cell in which thecolor filter order is BBGRRG-RGRBGB-GBRGRB-RRGBBG-BGBRGR-GRBGBR. In theoverlap area, R and B are sampled at a higher frequency than in astandard CFA. For example, in the overlap area pattern, R_(S) is 0.33vs. 0.25 in a Bayer pixel order.

FIG. 7 shows schematically an embodiment of a Wide sensor 700 that maybe implemented in a DAZI system such as system 100. Sensor 700 has anon-overlap area 702 with a Bayer CFA and an overlap area 704 covered bya non-standard CFA with a repetition of a 3×3 micro-cell in which thecolor filter order is GBR-RGB-BRG. In the overlap area, R and B aresampled at a higher frequency than in a standard CFA. For example, inthe overlap area pattern, R_(S) is 0.33 vs. 0.25 in a Bayer pixel order.

FIG. 8 shows schematically an embodiment of a Wide sensor 800 that maybe implemented in a DAZI system such as system 100. Sensor 800 has anon-overlap area 802 with a Bayer CFA and an overlap area 804 covered bya non-standard CFA with a repetition of a 6×6 micro-cell in which thecolor filter order is RBBRRB-RGRBGB-BBRBRR-RRBRBB-BGBRGR-BRRBBR. In theoverlap area, R and B are sampled at a higher frequency than in astandard CFA. For example, in the overlap area pattern, R_(S) is 0.44vs. 0.25 in a Bayer pixel order.

FIG. 9 shows schematically an embodiment of a Wide sensor 900 that maybe implemented in a DAZI system such as system 100. Sensor 900 has anon-overlap area 902 with a Bayer CFA and an overlap area 904 covered bya non-standard CFA with a repetition of a 6×6 micro-cell in which thecolor filter order is RBRBRB-BGBRGR-RBRBRB-BRBRBR-RGRBGB-BRBRBR. In theoverlap area, R and B are sampled at a higher frequency than in astandard CFA. For example, in the overlap area pattern, R_(S) is 0.44vs. 0.25 in a Bayer pixel order.

Processing Flow

In use, an image is acquired with imaging system 100 and is processedaccording to steps illustrated in a flowchart shown in FIG. 10. In step1000, demosaicing is performed on the Wide overlap area pixels (whichrefer to the Tele image FOV) according to the specific CFA pattern. Ifthe CFA in the Wide overlap area is a standard CFA, a standarddemosaicing process may be applied to it. If the CFA in the Wide overlaparea is non-standard CFA, the overlap and non-overlap subsets of pixelsmay need different demosaicing processes. That is, the Wide overlap areamay need a non-standard demosaicing process and the Wide non-overlaparea may need a standard demosaicing process. Exemplary and non-limitingnon-standard demosaicing interpolations for the overlap area of each ofthe Wide sensors shown in FIGS. 2-9 are given in detail below. The aimof the demosaicing is to reconstruct missing colors in each pixel.Demosaicing is applied also to the Tele sensor pixels if the Tele sensoris not a Clear only sensor. This will result in a Wide subset colorimage where the colors (in the overlap area) hold higher resolution thanthose of a standard CFA pattern. In step 1002, the Tele image isregistered (mapped) into the Wide image. The mapping includes findingcorrespondences between pixels in the two images. In step 1002, actualregistration is performed on luminance Tele and Wide images(respectively Luma_(Tele) and Luma_(Wide)) calculated from the pixelinformation of the Tele and Wide cameras. These luminance images areestimates for the scene luminance as captured by each camera and do notinclude any color information. If the Wide or Tele sensors have CFAs,the calculation of the luminance images is performed on the respectivedemosaiced images. The calculation of the Wide luminance image variesaccording to the type of non-standard CFA used in the Wide overlap area.If the CFA permits calculation of a full RGB demosaiced image, theluminance image calculation is straightforward. If the CFA is such thatit does not permit calculation of a full RGB demosaiced image, theluminance image is estimated from the available color channels. If theTele sensor is a Clear sensor, the Tele luminance image is just thepixel information. Performing the registration on luminance images hasthe advantage of enabling registration between images captured bysensors with different CFAs or between images captured by a standard CFAor non-standard CFA sensor and a standard CFA or Clear sensor andavoiding color artifacts that may arise from erroneous registration.

In step 1004, the data from the Wide and Tele images is processedtogether with the registration information from step 1002 to form a highquality output zoom image. In cases where the Tele sensor is a Clearonly sensor, the high resolution luminance component is taken from theTele sensor and color resolution is taken from the Wide sensor. In caseswhere the Tele sensor includes a CFA, both color and luminance data aretaken from the Tele subset to form the high quality zoom image. Inaddition, color and luminance data is taken from the Wide subset.

Exemplary Process for Fusing a Zoom Image

1. Special Demosaicing

In this step, the Wide image is interpolated to reconstruct the missingpixel values. Standard demosaicing is applied in the non-overlap area.If the overlap area includes a standard CFA, standard demosaicing isapplied there as well. If the overlap area includes a non-standard CFA,a special demosaicing algorithm is applied, depending on the CFA patternused. In addition, in case the Tele sensor has a CFA, standarddemosaicing is applied to reconstruct the missing pixel values in eachpixel location and to generate a full RGB color image.

2. Registration Preparation

-   -   Tele image: a luminance image Luma_(Tele) is calculated from the        Tele sensor pixels. If the Tele subset has a Clear sensor,        Luma_(Tele) is simply the sensor pixels data. If the Tele subset        has a standard CFA, Luma_(Tele) is calculated from the        demosaiced Tele image.    -   Wide image: as a first step, in case the Wide overlap CFA        permits estimating the luminance component of the image, the        luminance component is calculated from the demosaiced Wide        image, Luma_(Wide). If the CFA is one of those depicted in FIGS.        4-9, a luminance image is calculated first. If the CFA is one of        the CFAs depicted in FIG. 2 or FIG. 3, a luminance image is not        calculated. Instead, the following registration step is        performed between a weighted average of the demosaiced channels        of the Wide image and Luma_(Tele). For convenience, this        weighted average image is also denoted Luma_(Wide). For example,        if the Wide sensor CFA in the overlap region is as shown in FIG.        2, the demosaiced channels R_(Wide) and B_(Wide) are averaged to        create Luma_(Wide) according to        Luma_(Wide)=(f1*R_(Wide)+f2*B_(Wide))/(f1+f2), where f1 may be        f1=1 and f2 may be f2=1.    -   Low-pass filtering is applied on the Tele luminance image in        order to match its spatial frequency content to that of the        Luma_(Wide) image. This improves the registration performance,        as after low-pass filtering the luminance images become more        similar. The calculation is Luma_(Tele)→Low pass        filter→Luma_(Tele) ^(LP), where “LP” denotes an image after low        pass filtering.        3. Registration of Luma_(Wide) and Luma_(Tele) ^(LP)

This step of the algorithm calculates the mapping between the overlapareas in the two luminance images. The registration step does not dependon the type of CFA used (or the lack thereof), as it is applied onluminance images. The same registration step can therefore be applied onWide and Tele images captured by standard CFA sensors, as well as by anycombination of CFAs or Clear sensor pixels disclosed herein. Theregistration process chooses either the Wide image or the Tele image tobe a primary image. The other image is defined as an auxiliary image.The registration process considers the primary image as the baselineimage and registers the overlap area in the auxiliary image to it, byfinding for each pixel in the overlap area of the primary image itscorresponding pixel in the auxiliary image. The output image point ofview is determined according to the primary image point of view (cameraangle). Various correspondence metrics could be used for this purpose,among which are a sum of absolute differences and correlation.

In an embodiment, the choice of the Wide image or the Tele image as theprimary and auxiliary images is based on the ZF chosen for the outputimage. If the chosen ZF is larger than the ratio between thefocal-lengths of the Tele and Wide cameras, the Tele image is set to bethe primary image and the Wide image is set to be the auxiliary image.If the chosen ZF is smaller than or equal to the ratio between thefocal-lengths of the Tele and Wide cameras, the Wide image is set to bethe primary image and the Tele image is set to be the auxiliary image.In another embodiment independent of a zoom factor, the Wide image isalways the primary image and the Tele image is always the auxiliaryimage. The output of the registration stage is a map relating Wide imagepixels indices to matching Tele image pixels indices.

4. Combination into a High Resolution Image

In this final step, the primary and auxiliary images are used to producea high resolution image. One can distinguish between several cases:

a. If the Wide image is the primary image, and the Tele image wasgenerated from a Clear sensor, Luma_(Wide) is calculated and replaced oraveraged with Luma_(Tele) in the overlap area between the two images tocreate a luminance output image, matching corresponding pixels accordingto the registration map Luma_(Out)=c1*Luma_(Wide)+c2*Luma_(Tele). Thevalues of c1 and c2 may change between different pixels in the image.Then, RGB values of the output are calculated from Luma_(Out) andR_(Wide), G_(Wide), and B_(Wide).

b. If the Wide image is the primary image and the Tele image wasgenerated from a CFA sensor, Luma_(Tele) is calculated and is combinedwith Luma_(Wide) in the overlap area between the two images, accordingto the flow described in 4 a.

c. If the Tele image is the primary image generated from a Clear sensor,the RGB values of the output are calculated from the Luma_(Tele) imageand R_(Wide), G_(Wide), and B_(Wide) (matching pixels according to theregistration map).

d. If the Tele image is the primary image generated from a CFA sensor,the RGB values of the output (matching pixels according to theregistration map) are calculated either by using only the Tele imagedata, or by also combining data from the Wide image. The choice dependson the zoom factor.

Certain portions of the registered Wide and Tele images are used togenerate the output image based on the ZF of the output image. In anembodiment, if the ZF of the output image defines a FOV smaller than theTele FOV, the fused high resolution image is cropped to the requiredfield of view and digital interpolation is applied to scale up the imageto the required output image resolution.

Exemplary and Non-Limiting Pixel Interpolations Specifications for theOverlap Area

FIG. 2

B11 B12 R13 R21 B22 B23 R31 R32 B33In order to reconstruct the missing R22 pixel, we performR22=(R31+R13)/2. The same operation is performed for all missing Bluepixels.FIG. 3

R11 B12 R13 B21 R22 B23 R31 B32 R33In order to reconstruct the missing B22 pixel, we performB22=(B12+B21+B32+B23)/4. The same operation is performed for all missingRed pixels.FIG. 4

Y11 C12 Y13 C21 Y22 C23 Y31 C32 Y33In order to reconstruct the missing C22 pixel, we performC22=(C12+C21+C32+C23)/4. The same operation is performed for all missingYellow pixels.FIG. 5Case 1: W is Center Pixel

R11 B12 B13 R21 W22 R23 B31 B32 R33In order to reconstruct the missing 22 pixels, we perform the following:

B22=(B12+B32)/2

R22=(R21+R23)/2

G22=(W22−R22−B22) (assuming that W includes the same amount of R, G andB colors).

Case 2: R22 is Center Pixel

B11 B12 R13 R14 W21 R22 B23 W24 B31 R32 B33 R34In order to reconstruct the missing 22 pixels, we perform the following:

B22=(B11+R33)/2

W22=(2*W21+W24)/3

G22=(W22−R22−B22) (assuming that W contains the same amount of R, G andB colors). The same operation is performed for Blue as the center pixel.

FIG. 6

B11 B12 G13 R14 R21 G22 R23 B24 G31 B32 R33 G34 R41 R42 G43 B44In order to reconstruct the missing 22 pixels, we perform the following:

B22=(B12+B32)/2

R22=(R21+R23)/2.

In order to reconstruct the missing 32 pixels, we perform the following:

G32=(2*G31+2*G22+G43)/5

R32=(R41+2*R42+2*R33+R23+R21)/7.

FIG. 7

G11 B12 R13 G14 R21 G22 B23 R24 B31 R32 G33 B34 G41 B42 R43 G44In order to reconstruct the missing 22 pixels, we perform the following:

B22=(2*B12+2*B23+B31)/5

R22=(2*R21+2*R32+R13)/5

and similarly for all other missing pixels.

FIG. 8

R11 B12 B13 R14 R21 G22 R23 B24 B31 B32 R33 B34 R41 R42 B43 R44 B51 G52B53 R54In order to reconstruct the missing 22 pixels, we perform the following:

B22=(2*B12+2*B32+B13)/5

R22=(2*R21+2*R23+R11)/5.

In order to reconstruct the missing 32 pixels, we perform the following:

G32=(2*G22+G52)/3

R32=(2*R33+2*R42+R41+R21+R23)/7.

FIG. 9

R11 B12 R13 B14 B21 G22 B23 R24 R31 B32 R33 B34 B41 R42 B43 R44 R51 G52R53 B54In order to reconstruct the missing 22 pixels, we perform the following:

B22=(B12+B32+B23+B21)/4

R22=(R11+R13+R31+R33)/4.

In order to reconstruct the missing 32 pixels, we perform the following:

G32=(2*G22+G52)/3

R32=(R42+R31+R33)/3.

Triple-Aperture Zoom Imaging System with Improved Color Resolution

As mentioned, a multi-aperture zoom or non-zoom imaging system disclosedherein may include more than two apertures. A non-limiting and exemplaryembodiment 1100 of a triple-aperture imaging system is shown in FIGS.11A-11B. System 1100 includes a first Wide subset camera 1102 (withexemplarily X1), a second Wide subset camera (with exemplarily X1.5, andreferred to as a “Wide-Tele” subset) and a Tele subset camera (withexemplarily X2). FIG. 11A shows exemplary images captured by imagingsystem 1100, while FIG. 11B illustrates schematically three sensorsmarked 1102, 1104 and 1106, which belong respectively to the Wide,Wide-Tele and Tele subsets. FIG. 11B also shows the CFA arrangements ineach sensor: sensors 1102 and 1104 are similar to Wide sensors describedabove with reference to any of FIGS. 2-9, in the sense that they includean overlap area and a non-overlap area. The overlap area includes anon-standard CFA. In both Wide sensors, the non-overlap area may have aClear pattern or a standard CFA. Thus, neither Wide subset is solely aClear channel camera. The Tele sensor may be Clear or have a standardBayer CFA or a standard non-Bayer CFA. In use, an image is acquired withimaging system 1100 and processed as follows: demosaicing is performedon the overlap area pixels of the Wide and Wide-Tele sensors accordingto the specific CFA pattern in each overlap area. The overlap andnon-overlap subsets of pixels in each of these sensors may needdifferent demosaicing. Exemplary and non-limiting demosaicingspecifications for the overlap area for Wide sensors shown in FIGS. 2-9are given above. The aim is to reconstruct the missing colors in eachand every pixel. In cases in which the Tele subset sensor is not Clearonly, demosaicing is performed as well. The Wide and Wide-Tele subsetcolor images acquired this way will have colors (in the overlap area)holding higher resolution than that of a standard CFA pattern. Then, theTele image acquired with the Tele sensor is registered (mapped) into therespective Wide image. The data from the Wide, Wide-Tele and Tele imagesis then processed to form a high quality zoom image. In cases where theTele subset is Clear only, high Luma resolution is taken from the Telesensor and color resolution is taken from the Wide sensor. In caseswhere the Tele subset includes a CFA, both color and Luma resolution istaken from the Tele subset. In addition, color resolution is taken fromthe Wide sensor. The resolution of the fused image may be higher thanthe resolution of both sensors.

While this disclosure has been described in terms of certain embodimentsand generally associated methods, alterations and permutations of theembodiments and methods will be apparent to those skilled in the art.For example, multi-aperture imaging systems with more than two Wide orWide-Tele subsets (and sensors) or with more than one Tele subset (andsensor) may be constructed and used according to principles set forthherein. Similarly, non-zoom multi-aperture imaging systems with morethan two sensors, at least one of which has a non-standard CFA, may beconstructed and used according to principles set forth herein. Thedisclosure is to be understood as not limited by the specificembodiments described herein, but only by the scope of the appendedclaims.

The invention claimed is:
 1. A multi-aperture imaging system comprising:a) a first camera that provides a first image, the first camera having afirst field of view (FOV₁) and a first sensor with a first plurality ofsensor pixels covered at least in part with a standard color filterarray (CFA); b) a second camera that provides a second image, the secondcamera having a second field of view (FOV₂) such that FOV₂<FOV₁ and asecond sensor with a second plurality of sensor pixels, the secondplurality of sensor pixels being either Clear or covered with a standardCFA, the second image having an overlap area with the first image; andc) a processor configured to provide an output image from a point ofview of the first camera based on a zoom factor (ZF) input that definesa respective field of view (FOV_(ZF)), the first image being a primaryimage and the second image being a non-primary image, wherein ifFOV₂<FOV_(ZF)<FOV₁ then the point of view of the output image is that ofthe first camera, the processor further configured to register theoverlap area of the second image as non-primary image to the first imageas primary image to obtain the output image.
 2. The multi-apertureimaging system of claim 1, wherein, if FOV₂≧FOV_(ZF), then the processoris further configured to provide an output image from a point of view ofthe second camera.
 3. A method of acquiring images by a multi-apertureimaging system, the method comprising: a) providing a first imagegenerated by a first camera of the imaging system, the first camerahaving a first field of view (FOV₁) and a first sensor with a firstplurality of sensor pixels covered at least in part with a standardcolor filter array (CFA); b) providing a second image generated by asecond camera of the imaging system, the second camera having a secondfield of view (FOV₂) such that FOV₂<FOV and a second sensor with asecond plurality of sensor pixels, the second plurality of sensor pixelsbeing either Clear or covered with a standard CFA, the second imagehaving an overlap area with the first image; c) using a processor toprovide an output image from a point of view of the first camera basedon a zoom factor (ZF) input that defines a respective field of view(FOV_(ZF)), the first image being a primary image and the second imagebeing a non-primary image, wherein if FOV₂<FOV_(ZF)<FOV₁ then the pointof view of the output image is that of the first camera; and d) usingthe processor to register the overlap area of the second image asnon-primary image to the first image as primary image to obtain theoutput image.
 4. The method of claim 3, further comprising, ifFOV₂≧FOV_(ZF), using the processor to provide an output image from apoint of view of the second camera.